With the rapid development of the scale and speed of underground works, an increasing number of underground works such as coal mine roadways, highway and railway tunnels and large hydropower stations are being constructed with increasing newer and higher requirements on tunnel support. It can be expected in the coming decades that a large number of tunnels having such distinct characteristics as large section, large burial depth, high stress, long tunnel line and soft-fractured surrounding rock will be constructed under complex geological conditions, and the safety and stability problems of long-span tunnels under the circumstance of weak-broken surrounding rock are becoming increasingly serious.
For the characteristics of big deformation and difficulties in support of traditional deep soft rock chambers, special researches have been made on the patterns of support for large section chambers with deep high-stress soft rock at home and abroad, which have gone through traditional forms such as traditional bolt-shotcrete support, steel fiber reinforced shotcrete support and flexible steel bracket support to the form of bolt-mesh-shotcrete and flexible steel bracket combined support, etc. These support forms, however, often produce support effects that are not obvious, and mostly are insufficient in support resistance and not high in support strength.
In general, tunnel support under the conditions of deep high stress soft rock and fractured rock mass exhibits the problems of big deformation and difficulties in support. The prior art can hardly meet the support requirements of underground works such as roadways and tunnels with complex geological conditions, thereby seriously affecting the production and safety of the underground works. Therefore, there is now an urgent need for a new high-strength support system capable of effectively controlling deformation of the large section with large section and fractured surrounding rock.
Chinese patent application No. 2012103596417 entitled “Three-Dimensional Prestressed Steel Strand Backfilling Bracket Support System for Deep Soft Rock Roadway” provides a support system. Such a support system, unfortunately, is limited to a range of applications in roadways without solving the technical problem of big deformation of soft-fractured surrounding rock that soft rock tunnel construction faces. This invention may have the following disadvantages: in the event of tunnel crossing soft-fractured surrounding rock, excavation disturbance will inevitably cause big surrounding rock deformation, which may eventually result in tunnel face instability and tunnel collapse due to insufficient supporting force and consequent heavy economic losses.